Luteibacter jiangsuensis blood stream infection: a first case report

Background Luteibacter jiangsuensis is a gram-negative aerobic bacillus that was first isolated from soil samples at a pesticide factory in China and reported in 2011. Here, we describe the first case of L. jiangsuensis infection in human. Case presentation A 59-year-old Japanese woman undergoing treatment for Crohn’s disease was admitted to our hospital with fever. Clinical examination indicated catheter-related bloodstream infection. The catheter was removed and meropenem was initiated. Morphologically identical glucose non-fermentative gram-negative bacilli were detected from two sets of aerobic blood culture and catheter-tip cultures. MALDI-TOF mass spectrometry failed to identify the bacterium, which was later identified as L. jiangsuensis by 16 S rRNA gene sequencing. Antimicrobial susceptibility test revealed that the isolate was resistant to carbapenem, therefore meropenem was switched to intravenous levofloxacin (500 mg/day). After 14 days of treatment with levofloxacin, the patient was discharged. Conclusions This is the first case of L. jiangsuensis infection in human. The strain was identified by 16 S rRNA gene sequence analysis.


Background
Luteibacter jiangsuensis is a gram-negative aerobic bacillus in the genus Luteibacter of the family Rhodanobacteraceae.L. jiangsuensis (strain JW-64-1 T ) was first isolated in 2011 from soil samples taken from a pesticide (methamidophos)-manufacturing factory in China [1], but there have been no reports of human L. jiangsuensis infections, and its pathogenicity to humans is unknown.
A physical examination revealed swelling and redness around the CV port insertion site.A contrast-enhanced computed tomography examination showed a 10-mm hypodense lesion at the tip of the CV catheter in the superior vena cava (Fig. 1).The results of blood tests were as follows: white blood cell count, 4.0 × 10 9 /L; neutrophil percentage, 48.0%; absolute neutrophil count, 1.9 × 10 9 /L; C-reactive protein, 60.1 mg/L; procalcitonin, 0.43 ng/mL; albumin, 3.6 g/dL; blood urea nitrogen, 9.9 mg/ dL; and creatinine, 0.90 mg/dL.Two sets of aerobic and anaerobic blood cultures were submitted, and treatment was initiated with meropenem (1 g, thrice daily).On day 2 of hospitalization, the CV port/catheter was removed, and the catheter tip was submitted for two sets of culture testing.The patient's fever drastically improved after initial treatment.On day 3, gram-negative rod bacteria were detected from both sets of aerobic blood culture at 31 and 36 h (anaerobic culture was negative).The same bacterium was also detected from the catheter-tip culture, and its morphology was suggestive of glucose non-fermentative bacilli.On day 6, drug susceptibility results (Table 1) revealed carbapenem resistance, therefore meropenem was switched to levofloxacin 500 mg/day by intravenous infusion.After 14 days of treatment with levofloxacin, CV port/catheter was placed, and the patient was discharged on day 18 of hospitalization (Fig. 2).
Regarding the identification of bacterial species, the top 3 matches and scores given by Matrix-assisted laser MICs were determined using the broth microdilution method.The SIR was determined using CLSI breakpoints (glucose non-fermenting bacteria) jiangsuensis isolate was Gram-negative, aerobic, sporefree, rod-shaped bacteria (Fig. 3A) and produced circular, smooth, grey-colored colonies (2-3 mm) on Sheep Blood Agar (T) and green-colored colonies (3-4 mm) on Drigalski Lactose Agar after 24 h incubation (Fig. 3B).Biochemical characteristics of the strain isolated from the present patient were similar to those of strain JW-64-1 T except for catalase activity, acid production from glucose and lactose, and nitrate reduction (Table 2).Although strain JW-64-1 T can reduce nitrate to nitrite, our strain could not reduce nitrate consistent with other Luteibacter spp.[1].Antimicrobial susceptibility test of the isolate revealed high minimum inhibitory concentration (MIC) values for first to third generation cephalosporins and carbapenems (Table 1).

Discussion and conclusions
We report the first case of CRBSI caused by L. jiangsuensis.The genus Luteibacter was first reported and established by Johansen et al. in 2005 [2].Although the genus was originally thought to belong to the family Xanthomonadaceae in the class Gammaproteobacteria, genomic analysis revealed that it is in the family Rhodanobacteraceae [3].To our knowledge, only two clinical cases of the genus Luteibacter infection in humans have been reported: CRBSI caused by L. anthropi [4] and a Luteibacter sp., which shared 97.4% identity with L. rhizovicina [5].The present case is the first report of L. jiangsuensis infection in humans.Luteibacter spp. is found primarily in environmental soil.L. jiangsuensis has the capacity to grow at 4-42 ℃ (optimum temperature 37 ℃) and pH 4.5-8.0(optimum pH 7.0).L. jiangsuensis can hydrolyze and utilize substrates of organic compounds, including carbohydrates.However, the pathogenicity of L. jiangsuensis in mammals is unknown due to the absence of clinical and experimental data.The patient in this report had no exposure to soil or any other suspected sources of infection.Like our present patient, the individual with bacteremia caused by a Luteibacter sp. also had CV catheter and was immunocompromised due to hematological disorder and chemotherapy [5].We thus speculate that malnutrition from Crohn's disease, the use of immunosuppressive drugs, and CV catheter placement may have been the risk factors for our patient's Luteibacter bacteremia.
In vitro susceptibility testing showed that the isolate was carbapenem resistant, yet treatment with meropenem appeared to be effective (Fig. 2).The removal of CV port/catheter was considered a major contributor to this favorable clinical course.The clinical breakpoints and the epidemiological cutoff values for Luteibacter spp.have not been established by the Clinical and Laboratory Standards Institute (CLSI) or the European Committee on Anti-microbial Susceptibility Testing.Therefore, we used the SIR breakpoints determined for "glucose non-fermenting bacteria" in CLSI.In the future, further studies including whole genome sequencing should be conducted to elucidate the mechanism of drug resistance of this isolate.
For antimicrobial susceptibility testing, bacterial strains were incubated at 35 ℃ for 18 h and minimal inhibitory concentrations (MICs) were determined using MicroScan WalkAway-96 plus with Neg MIC 3 J panel (Beckman Coulter, CA, USA) according to the manufacturer's instruction.The SIR (susceptible/intermediate/ resistant) was determined according to the criteria of CLSI M100-30th edition for glucose non-fermenting bacteria [6].

Luteibacter jiangsuensis isolate
Oxidase activity was evaluated using Cytochrome Oxidase Test Strip (Shimadzu Diagnostics, Tokyo, Japan).Catalase activity was evaluated using 3% hydrogen peroxide (Fujifilm Wako Chemicals, Osaka, Japan) as described

Fig. 1
Fig. 1 Contrast-enhanced computed tomography image on admission.Black arrow: central venous catheter placed in the superior vena cava.White arrow: a 10-mm-diameter hypodense lesion adjacent to the catheter

Table 2
Biochemical characteristics of the Luteibacter jiangsuensis isolateAll items were evaluated using ID test NF-18 (Shimadzu Diagnostics, Tokyo, Japan) in this study except the followings 1 Evaluated using Cytochrome Oxidase Test Strip (Shimadzu Diagnostics)2Evaluated using 3% hydrogen peroxide (Fujifilm Wako Chemicals, Osaka, Japan)